**Ten algorithms for Egyptian fractions**.

D. Eppstein.

*Mathematica in Education and Research*4 (2): 5–15, 1995.Number theory. I survey and implement in

*Mathematica*several methods for representing rational numbers as sums of distinct unit fractions. One of the methods involves searching for paths in a certain graph using a*k*shortest paths heuristic.(BibTeX – Citations – Also available in HTML and Mathematica notebook formats)

**Finding the**.*k*shortest paths

D. Eppstein.

*35th IEEE Symp. Foundations of Comp. Sci.,*Santa Fe, 1994, pp. 154–165.

Tech. Rep. 94-26, ICS, UCI, 1994.

*SIAM J. Computing*28 (2): 652–673, 1998.This paper presents an algorithm that finds multiple short paths connecting two terminals in a graph (allowing repeated vertices and edges in the paths) in constant time per path after a preprocessing stage dominated by a single-source shortest path computation. The paths it finds are the

*k*shortest in the graph, where*k*is a parameter given as input to the algorithm.The

*k*shortest paths problem has many important applications for finding alternative solutions to geographic path planning problems, network routing, hypothesis generation in computational linguistics, and sequence alignment and metabolic pathway finding in bioinformatics. Although there have been many papers on the*k*shortest paths problem before and after this one, it has become frequently cited in those application areas. Additionally, it marks a boundary in the theoretical study of the problem: prior theoretical work largely concerned how quickly the problem could be solved, a line of research that was closed off by the optimal time bounds of this paper. Subsequent work has focused instead on devising efficient algorithms for more complex alternative formulations of the problem that avoid the repeated vertices and other shortcomings of the alternative paths produced by this formulation.(BibTeX – Full paper – Citations – Graehl implementation – Jiménez-Marzal implementations – Shibuya implementation – Martins implementation – Cliff OpenStreetMap demo – CiteSeer: TR '94, SJC '98 – ACM DL)

**Representing all minimum spanning trees with applications to counting and generation**.

D. Eppstein.

Tech. Rep. 95-50, ICS, UCI, 1995.Shows how to find for any edge weighted graph G an equivalent graph EG such that the minimum spanning trees of G correspond one-for-one with the spanning trees of EG. The equivalent graph can be constructed in time O(m+n log n) given a single minimum spanning tree of G. As a consequence one can find fast algorithms for counting, listing, and randomly generating MSTs. Also discusses similar equivalent graph constructions for shortest paths, minimum cost flows, and bipartite matching.

**Finding common ancestors and disjoint paths in DAGs**.

D. Eppstein.

Tech. Rep. 95-52, ICS, UCI, 1995.This paper describes algorithms for finding pairs of vertex-disjoint paths in a DAG, either connecting two given nodes to a common ancestor, or connecting two given pairs of terminals. The main results were merged into the journal version of "Finding the

*k*shortest paths".(BibTeX)

**Beta-skeletons have unbounded dilation**.

D. Eppstein.

Tech. Rep. 96-15, ICS, UCI, 1996.

arXiv:cs.CG/9907031.

*Comp. Geom. Theory & Applications*23: 43–52, 2002.Beta-skeletons are geometric graphs used among other purposes for empirical network analysis and minimum weight triangulation. A fractal construction shows that, for any beta>0, the beta-skeleton of a point set can have arbitrarily large dilation: Omega(n

^{c}), where c is a constant depending on beta and going to zero in the limit as beta goes to zero. In particular this applies to the Gabriel graph. We also show upper bounds on dilation of the same form.**Spanning trees and spanners**.

D. Eppstein.

Tech. Rep. 96-16, ICS, UCI, 1996.

*Handbook of Computational Geometry,*J.-R. Sack and J. Urrutia, eds., Elsevier, 1999, pp. 425–461.Surveys results in geometric network design theory, including algorithms for constructing minimum spanning trees and low-dilation graphs.

(BibTeX – Citations – CiteSeer)

**An efficient algorithm for shortest paths in vertical and horizontal segments**.

D. Eppstein and D. Hart.

*5th Worksh. Algorithms and Data Structures,*Halifax, Nova Scotia, 1997.

Springer,*Lecture Notes in Comp. Sci.*1272, 1997, pp. 234–247.We show how to find shortest paths along the segments of an arrangement of

*n*vertical and horizontal line segments in the plane, in time O(*n*^{3/2}).(BibTeX – Citations – CiteSeer – ACM DL)

**Diameter and treewidth in minor-closed graph families**.

D. Eppstein.

arXiv:math.CO/9907126.

*Algorithmica*27: 275–291, 2000 (special issue on treewidth, graph minors, and algorithms).This paper introduces the

*diameter-treewidth property*(later known as*bounded local treewidth*): a functional relationship between the diameter of its graph and its treewidth. Previously known results imply that planar graphs have bounded local treewidth; we characterize the other minor-closed families with this property. Specifically, minor-closed family F has bounded local treewidth if and only if there exists an*apex graph*G that is not in F; an apex graph is a graph that can be made planar by removing a single vertex. The minor-free families that exclude an apex graph (and therefore have bounded local treewidth) include the bounded-genus graphs (for which, as with planar graphs, we show a linear bound for the treewidth as a function of the diameter) and K_{3,a}-free graphs. As a consequence, subgraph isomorphism for subgraphs of bounded size and approximations to several NP-hard optimization problems can be computed efficiently on these graphs, extending previous results for planar graphs.Some of these results were announced in the conference version of "subgraph isomorphism for planar graphs and related problems" but not included in the journal version. Since its publication, there have been many more works on local treewidth. The class of problems that could be solved quickly on graphs of bounded local treewidth was extended and classified by Frick and Grohe, "Deciding first-order properties of locally tree-decomposable structures",

*J. ACM*48: 1184–1206, 2001; the proof that bounded local treewidth is equivalent to having an excluded apex minor was simplified, and the dependence of the treewidth on diameter improved, by a subsequent paper of Demaine and Hajiaghayi, "Diameter and treewidth in minor-closed graph families, revisited",*Algorithmica*40: 211–215, 2004. The concept of local treewidth is the basis for the theory of*bidimensionality*, a general framework for fixed-parameter-tractable algorithms and approximation algorithms in minor-closed graph families; for a survey, see Demaine and Hajiaghayi, "The bidimensionality theory and its algorithmic applications",*The Computer J.*51: 292–302, 2008.**Shortest paths in an arrangement with**.*k*line orientations

D. Eppstein and D. Hart.

*10th ACM-SIAM Symp. Discrete Algorithms,*Baltimore, 1999, pp. 310–316.We show how to find shortest paths between two points on the lines of an arrangement of

*n*lines with*k*distinct orientations, in time O(*n*+*k*^{2}).(BibTeX – SODA paper – Citations – CiteSeer)

**Setting parameters by example**.

D. Eppstein.

arXiv:cs.DS/9907001.

*40th IEEE Symp. Foundations of Comp. Sci.*, 1999, pp. 309–318.

*SIAM J. Computing*32 (3): 643–653, 2003.We introduce a class of "inverse parametric optimization" problems, in which one is given both a parametric optimization problem and a desired optimal solution; the task is to determine parameter values that lead to the given solution. We use low-dimensional linear programming and geometric sampling techniques to solve such problems for minimum spanning trees, shortest paths, and other optimal subgraph problems, and discuss applications in multicast routing, vehicle path planning, resource allocation, and board game programming.

(BibTeX – Citations – ACM DL (FOCS) – ACM DL (SJC))

**Searching for spaceships**.

D. Eppstein.

arXiv:cs.AI/0004003.

MSRI Combinatorial Game Theory Research Worksh., July 2000.

*More Games of No Chance*, R. J. Nowakowski, ed., MSRI Publications 42, pp. 433–453.We describe software that searches for spaceships in Conway's Game of Life and related two-dimensional cellular automata. Our program searches through a state space related to the de Bruijn graph of the automaton, using a method that combines features of breadth first and iterative deepening search, and includes fast bit-parallel graph reachability and path enumeration algorithms for finding the successors of each state. Successful results include a new 2c/7 spaceship in Life, found by searching a space with 2^126 states.

(BibTeX – MSRI talk on streaming video and Slides – Citations – CiteSeer)

**One-dimensional peg solitaire, and duotaire**.

C. Moore and D. Eppstein.

arXiv:math.CO/0006067 and math.CO/0008172.

MSRI Combinatorial Game Theory Research Worksh., July 2000.

Santa Fe Inst. working paper 00-09-050, September 2000.

*More Games of No Chance*, R. J. Nowakowski, ed., MSRI Publications 42, pp. 341–350.We describe by a regular expression the one-dimensional peg-solitaire positions reducible to a single peg, and provide a linear-time algorithm (based on finding shortest paths in an associated DAG) for reducing any such position to the minimum number of pegs. We then investigate impartial games in which players alternate peg solitaire moves in an attempt to be the one to move last.

(BibTeX – Citations – Cris' MSRI talk on streaming video – Cris' publications page – CiteSeer)

**Phutball endgames are hard**.

E. Demaine, M. Demaine, and D. Eppstein.

arXiv:cs.CC/0008025.

*More Games of No Chance*, R. J. Nowakowski, ed., MSRI Publications 42, pp. 351–360.We show that, in John Conway's board game Phutball (or Philosopher's Football), it is NP-complete to determine whether the current player has a move that immediately wins the game. In contrast, the similar problems of determining whether there is an immediately winning move in checkers, or a move that kings a man, are both solvable in polynomial time.

(BibTeX – Citations – Erik's publications page – CiteSeer)

**Fast approximation of centrality**.

D. Eppstein and J. Wang.

arXiv:cs.DS/0009005.

*12th ACM-SIAM Symp. Discrete Algorithms,*Washington, 2001, pp. 228–229.

*J. Graph Algorithms & Applications*8 (1): 39–45, 2004.We use random sampling to quickly estimate, for each vertex in a graph, the average distance to all other vertices.

(BibTeX – SODA paper – Citations – CiteSeer)

**Nonrepetitive paths and cycles in graphs with application to Sudoku**.

D. Eppstein.

arXiv:cs.DS/0507053.We describe algorithms and hardness results for finding paths in edge-labeled graphs such that no two consecutive edges have the same label, and use our algorithms to implement heuristics for a program that automatically solves and generates Sudoku puzzles.

**Succinct greedy geometric routing using hyperbolic geometry**.

D. Eppstein and M. T. Goodrich.

arXiv:0806.0341.

*Proc. 16th Int. Symp. Graph Drawing*, Heraklion, Crete, 2008

(under the different title "Succinct greedy graph drawing in the hyperbolic plane"),

Springer,*Lecture Notes in Comp. Sci.*5417, 2009, pp. 14–25.

*IEEE Transactions on Computing*60 (11): 1571–1580, 2011.Greedy drawing is an idea for encoding network routing tables into the geometric coordinates of an embedding of the network, but most previous work in this area has ignored the space complexity of these encoded tables. We refine a method of R. Kleinberg for embedding arbitrary graphs into the hyperbolic plane, which uses linearly many bits to represent each vertex, and show that only logarithmic bits per point are needed.

**Studying (non-planar) road networks through an algorithmic lens**.

D. Eppstein, and M. T. Goodrich.

arXiv:0808.3694.

*Proc. 16th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems (ACM GIS 2008)*, Article 16 (best paper award).

Invited talk at INFORMS 2009, San Diego.We examine US road network data and show that, contrary to the assumptions of much past GIS work, these networks are highly nonplanar. We introduce a class of "multiscale dispersed" networks that better fit the data; these networks are defined by a family of disks of varying sizes such that, if a small number of outliers is removed, the remaining disks cover each point of the plane a constant number of times. As we show, these networks have good graph separators, allowing for efficient algorithms for minimum spanning trees, graph Voronoi diagrams, and related problems.

**Linear-time algorithms for geometric graphs with sublinearly many crossings**.

D. Eppstein, M. T. Goodrich, and D. Strash.

arXiv:0812.0893.

*20th ACM-SIAM Symp. Discrete Algorithms,*New York, 2009, pp. 150–159.

*SIAM J. Computing*39 (8): 3814–3829, 2010.If a connected graph corresponds to a set of points and line segments in the plane, in such a way that the number of crossing pairs of line segments is sublinear in the size of the graph by an iterated-log factor, then we can find the arrangement of the segments in linear time. It was previously known how to find the arrangement in linear time when the number of crossings is superlinear by an iterated-log factor, so the only remaining open case is when the number of crossings is close to the size of the graph.

**Optimal angular resolution for face-symmetric drawings**.

D. Eppstein and K. Wortman.

arXiv:0907.5474.

*J. Graph Algorithms and Applications*15 (4): 551–564, 2011.We consider drawings of planar partial cubes in which all interior faces are centrally symmetric convex polygons, as in my previous paper Algorithms for Drawing Media. Among all drawings of this type, we show how to find the one with optimal angular resolution. The solution involves a transformation from the problem into the parametric negative cycle detection problem: given a graph in which the edge weights are linear functions of a parameter λ, find the minimum value of λ for which the graph contains no negative cycles.

**Category-based routing in social networks: membership dimension and the small-world phenomenon**.

D. Eppstein, M. T. Goodrich, M. Löffler, D. Strash, and L. Trott.

*Workshop on Graph Algorithms and Applications*, Zürich, Switzerland, July 2011.

*International Conference on Computational Aspects of Social Networks (CASoN 2011)*, Salamanca, Spain, October 2011.

arXiv:1108.4675.

*Theor. Comput. Sci.*514: 96–104, 2013. (Special issue on Graph Algorithms and Applications: in Honor of Professor Giorgio Ausiello)

We investigate greedy routing schemes for social networks, in which participants know categorical information about some other participants and use it to guide message delivery by forwarding messages to neighbors that have more categories in common with the eventual destination. We define the membership dimension of such a scheme to be the maximum number of categories that any individual belongs to, a natural measure of the cognitive load of greedy routing on its participants. And we show that membership dimension is closely related to the small world phenomenon: a social network can be given a category system with polylogarithmic membership dimension that supports greedy routing if, and only if, the network has polylogarithmic diameter.

**Randomized speedup of the Bellman–Ford algorithm**.

M. J. Bannister and D. Eppstein.

arXiv:1111.5414.

*Analytic Algorithmics and Combinatorics (ANALCO12)*, Kyoto, Japan, 2012, pp. 41–47.The Bellman–Ford algorithm for single-source shortest paths in graphs that may have negatively weighted edges but no negative cycles can be sped up by a technique of Yen in which the graph is partitioned into two directed acyclic subgraphs and edge relaxations alternate between these two subgraphs. We show that choosing this partition randomly gains an additional factor of 2/3 in running time.

**Solving single-digit Sudoku subproblems**.

D. Eppstein.

arXiv:1202.5074.

*6th International Conference on Fun with Algorithms (FUN 2012)*, Venice, Italy, 2012.

Springer,*Lecture Notes in Comp. Sci.*7288, 2012, pp. 142–153.We find an algorithm for making all possible deductions based on the set of candidate locations for a single digit in a Sudoku puzzle; the problem is NP-hard, and our algorithm takes exponential time, but the mild form of the exponential allows it to be fast for practical problem sizes.

(Slides)

**Near-linear-time deterministic plane Steiner spanners and TSP approximation for well-spaced point sets**.

G. Borradaile and D. Eppstein.

arXiv:1206.2254.

*24th Canadian Conference on Computational Geometry (CCCG 2012)*, Prince Edward Island, Canada, 2012, pp. 311–316.

*Comp. Geom. Theory & Applications*49: 8–16, 2015 (special issue for CCCG 2012).When a planar point set has the property that its Delaunay triangulation has no large angles, we show how to connect it by a plane graph (having linearly many additional Steiner vertices) in which the distances between the original points are approximations to their Euclidean distance, and in which the total graph weight is at most a constant times the minimum spanning tree weight. The time to construct this graph is near-linear, the same as for integer sorting. We use this result to approximate the traveling salesman problem, for these point sets, in the same time bound.

.*k*-best enumeration

D. Eppstein.

*Encyclopedia of Algorithms*(Ming-Yang Kao, ed.), Springer, added 2014.

arXiv:1412.5075.

*Bull. EATCS*115, 2015.A brief survey of algorithms for finding the

*k*shortest paths and related*k*-best enumeration problems. The arXiv/EATCS version is significantly longer and with more references than the Springer version.**Rooted cycle bases**.

D. Eppstein, J. M. McCarthy, and B. E. Parrish.

arXiv:1504.04931.

14th Algorithms and Data Structures Symp. (WADS 2015), Victoria, BC.

Springer,*Lecture Notes in Comp. Sci.*9214 (2015), pp. 339–350.

*J. Graph Algorithms & Applications*21 (4): 663–686, 2017.We consider the problem of finding a cycle basis for a graph in which all basis cycles contain a specified edge. We characterize the graphs having such a basis in terms of their vertex connectivity, we show that the minimum weight cycle basis with this constraint can be found in polynomial time and is weakly fundamental, and we show that finding a fundamental cycle basis with this constraint is NP-hard but fixed-parameter tractable.

(Slides)

**Approximate greedy clustering and distance selection for graph metrics**.

D. Eppstein, S. Har-Peled, and A. Sidiropoulos.

arXiv:1507.01555.

We provide fast approximation algorithms for the farthest-first traversal of graph metrics.

.*K*-best solutions of MSO problems on tree-decomposable graphs

D. Eppstein and D. Kurz.

arXiv:1703.02784.

*Proc. 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Vienna, Austria, 2017.

Leibniz International Proceedings in Informatics (LIPIcs) 89, pp. 16.1–16.13We show that, on graphs of bounded treewidth, for any optimization problem definable in monadic second-order logic, we can find the

*k*best solutions in logarithmic time per solution.**Crossing patterns in nonplanar road networks**.

D. Eppstein and S. Gupta.

arXiv:1709.06113.

*Proc. 25th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems (ACM SIGSPATIAL 2017)*, Redondo Beach, California, pp. 40:1–40:9.

We show that, although an individual edge in a road network can have many crossings, real-world road networks have the property that the crossing graph of their edges is sparse. We prove that networks with this property are themselves sparse and have small separators, allowing many fast algorithms to be generalized from planar graphs to these networks.

**Undirected path reconfiguration**.

E. Demaine, D. Eppstein, A. Hesterberg, K. Jain, A. Lubiw, R. Uehara, and Y. Uno.

*16th Algorithms and Data Structures Symp. (WADS 2019)*, Edmonton, Alberta.

Graph Theory – Publications – David Eppstein – Theory Group – Inf. & Comp. Sci. – UC Irvine

Semi-automatically filtered from a common source file.